MAX9726 Maxim Integrated Products, MAX9726 Datasheet - Page 18

• Manufacturer Part Number: MAX9726
• Description: Headphone Amplifier
• Manufacturer: Maxim Integrated Products

www.DataSheet4U.com
DataSheet U .com
4
The hold capacitor’s value and ESR directly affect the
ripple at PV
value of the hold capacitor. Choosing a capacitor with
lower ESR reduces ripple and output impedance.
Lower capacitance values can be used in systems with
low maximum output power levels. See the Output
Power vs. Charge-Pump Capacitance and Load
Resistance graphs in the Typical Operating
Characteristics. C2 should be greater than or equal to
the value of C1.
The AC-coupling capacitor (C
(R
from an input signal. See the Functional Diagram/
Typical Operating Circuit. C
nents from the input signal source from appearing in
the amplifier outputs. The -3dB point of the highpass fil-
ter, assuming zero-source impedance due to the input
signal source, is given by:
Choose C
quency of interest. Setting f
amplifier’s low-frequency response. Use capacitors with
low-voltage coefficient dielectrics. Aluminum electrolytic,
tantalum, or film dielectric capacitors are good choices
for AC-coupling capacitors. Capacitors with high-voltage
coefficients, such as ceramics (non-C0G dielectrics),
can result in increased distortion at low frequencies.
With BassMax disabled, the maximum gain of the
MAX9726 is set by the values of the external resistors
R
Operating Circuit). When BassMax is disabled, the
maximum gain of the MAX9726 is:
DirectDrive, Headphone Amplifier with
BassMax, I
18
IN
IN
) form a highpass filter that removes any DC bias
and R
______________________________________________________________________________________
IN
F
such that f
SS
(see the Functional Diagram/Typical
f
. Ripple is reduced by increasing the
−
A
3
dB
V
Charge-Pump Hold Capacitor (C2)
=
=
20 log
2π
-3dB
×
×
2
R
IN
Gain-Setting Components
is well below the lowest fre-
IN
Input-Coupling Capacitor
⎛
⎜
⎝
1
C, Volume and Gain Control
-3dB
R
R
prevents any DC compo-
×
IN
F
C
IN
⎞
⎟
⎠
IN
) and input resistor
too high affects the
(
dB
(
Hz
)
)
where A
all voltage gain of the MAX9726 with BassMax disabled
is equal to:
where ATTEN
ume setting in dB and A
gain of the MAX9726 in dB.
When BassMax is enabled, the bass-boost low-fre-
quency response is set by the ratio of R1 to R2, by the
following equation (see Figure 2):
where A
cies in dB. A
volume setting and the gain set by resistors R
(A
frequencies with BassMax enabled is equal to:
where A
low frequencies in dB.
To maintain circuit stability, the ratio
must not exceed one-half. A ratio equal to or less than
one-third is recommended. The switch that shorts BM_
to SGND, when BassMax is disabled, can have an on-
resistance as high as 300Ω. Choose a value for R1 that
is greater than 40kΩ to ensure that positive feedback is
negligible when BassMax is disabled. Table 7 contains
a list of R2 values, with R1 = 47kΩ, and the corre-
sponding low-frequency gain boost.
Table 7. BassMax Gain Examples
(R1 = 47kΩ)
V
). The overall voltage gain of the MAX9726 at low
A
TOTAL BB
R2 (kΩ)
V
BOOST
TOTAL_BB
39
33
27
22
15
10
A
is the maximum voltage gain in dB. The over-
TOTAL
A
_
BOOST
BOOST
dB_VOL
is the voltage gain boost at low frequen-
=
=
A
is the overall gain of the MAX9726 at
V
A
is added to the gain realized by the
LOW-FREQUENCY GAIN BOOST (dB)
=
V
+
is the attenuation due to the vol-
20
A
−
ATTEN
×
BOOST
TOTAL
log
⎛
⎜
⎝
R
R
dB VOL
1
1
−
+
is the overall voltage
−
ATTEN
_
R
R
20.6
15.1
11.3
2
8.8
5.7
3.7
2
⎞
⎟
⎠
(
(
dB
dB
dB VOL
)
)
_
IN
R
1
and R
(
R
dB
+
2
R
)
2
F